Feature: Implement multi-stage Conversation Flow Engine with TestFlow

backend/app/Core/Flows/BaseFlow.php

@@ -0,0 +1,20 @@
+<?php
+
+namespace App\Core\Flows;
+
+/**
+ * BaseFlow
+ * Abstract base class for all conversation flow states.
+ */
+abstract class BaseFlow
+{
+    /**
+     * Process a step in the conversation flow.
+     *
+     * @param string $step The current step identifier ('start' for new flows)
+     * @param array $messageData The incoming WhatsApp message payload (body, phone, etc.)
+     * @param array $context Reference to the persistent JSON context array
+     * @return FlowResult
+     */
+    abstract public function handleStep(string $step, array $messageData, array &$context): FlowResult;
+}